The present invention relates to high alumina refractory shapes and in particular bricks that are utilized primarily for aluminum furnaces.
At the present time, such refractory shapes, and particularly the bricks, show a susceptibility to penetration by the aluminum in the furnace. As a consequence, the refractory undergoes alteration and is ultimately consumed due, in part, to the penetration of the aluminum into the brick. Various efforts have been made to find suitable additives in order to improve the penetration resistance of high alumina bricks but these approaches have had limited success due to the undesired lowering of the hot strength of the refractory shape or brick or on the processing characteristics.
Such efforts have included; as in U.S. Pat. No. 4,088,502, the use of zinc borosilicate frit as a penetration inhibitor or in the case of U.S. Pat. No. 4,126,474 the use of barium sulfate. However, it has been found that addition of zinc borosilicate frit when used in combination with phosphoric acid which is utilized for maximum strength causes a severe degree of sticking to the press used in forming the shape of the brick to the point where it is not possible to get satisfactory brick in order to utilize them in aluminum furnaces. Addition of BaSo.sub.4 lowers the hot strength.